Conveyor belts include a core layer disposed between an upper cover rubber and a lower cover rubber that bears the tension when the conveyor belt is mounted in a tensioned state. Damage to the core layer makes it difficult for the conveyor belt to be mounted normally. Thus, to keep the conveyor belt operational, it is important to prevent damage to the core layer.
Object to be conveyed are fed onto the upper cover rubber, impacting upon the upper cover rubber with a force that is greater the higher the height from which they were feed or the greater the weight of the objects to be conveyed. Damage is accelerated by greater impacts, causing greater deformation in the upper cover rubber. Excessive damage to the upper cover rubber makes the core layer susceptible to damage. This in turn shortens the service life of the conveyor belt.
A structure is known in which a reinforcing layer is provided in an upper cover rubber to improve the heat resistance and the shock resistance of a conveyor belt (see Japanese Unexamined Patent Application Publication No. H2-261711). In this structure, the warp thread that composes the reinforcing layer has a lower elastic modulus in the length direction than the tension layer (core layer), and the weft thread has heat resistance and shock resistance. In other words, this disclosed technology is based on the reinforcing layer being composed of warp thread and weft thread, and other configurations are not considered. Additionally, by the warp thread having an elastic modulus in the length direction lower than that of the tension layer (core layer), excess bending rigidity is avoided when the conveyor belt bends.
However, by the warp thread having a reduced elastic modulus in the length direction, when the impact on the upper cover rubber is great, this force is dissipated less effectively. Accordingly, this structure has difficulty protecting the core layer from the impact of fed objects to be conveyed over an extended period of time, and thus is unsuited to lengthening the service life of the core layer.